<s>
An	O
organic	B-Algorithm
field-effect	I-Algorithm
transistor	I-Algorithm
(	O
OFET	B-Algorithm
)	O
is	O
a	O
field-effect	O
transistor	O
using	O
an	O
organic	B-Algorithm
semiconductor	I-Algorithm
in	O
its	O
channel	O
.	O
</s>
<s>
OFETs	B-Algorithm
can	O
be	O
prepared	O
either	O
by	O
vacuum	O
evaporation	O
of	O
small	O
molecules	O
,	O
by	O
solution-casting	O
of	O
polymers	B-Language
or	O
small	O
molecules	O
,	O
or	O
by	O
mechanical	O
transfer	O
of	O
a	O
peeled	O
single-crystalline	O
organic	O
layer	O
onto	O
a	O
substrate	O
.	O
</s>
<s>
OFETs	B-Algorithm
have	O
been	O
fabricated	O
with	O
various	O
device	O
geometries	O
.	O
</s>
<s>
Organic	O
polymers	B-Language
,	O
such	O
as	O
poly(methyl-methacrylate )	O
(	O
PMMA	O
)	O
,	O
can	O
also	O
be	O
used	O
as	O
dielectric	O
.	O
</s>
<s>
One	O
of	O
the	O
benefits	O
of	O
OFETs	B-Algorithm
,	O
especially	O
compared	O
with	O
inorganic	O
TFTs	O
,	O
is	O
their	O
unprecedented	O
physical	O
flexibility	O
,	O
which	O
leads	O
to	O
biocompatible	O
applications	O
,	O
for	O
instance	O
in	O
the	O
future	O
health	O
care	O
industry	O
of	O
personalized	O
biomedicines	O
and	O
bioelectronics	O
.	O
</s>
<s>
The	O
first	O
insulated-gate	B-Architecture
field-effect	I-Architecture
transistor	I-Architecture
was	O
designed	O
and	O
prepared	O
by	O
Mohamed	O
Atalla	O
and	O
Dawon	O
Kahng	O
at	O
Bell	O
Labs	O
using	O
a	O
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
semiconductor	I-Architecture
:	O
the	O
MOSFET	B-Architecture
(	O
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
semiconductor	I-Architecture
field-effect	I-Architecture
transistor	I-Architecture
)	O
.	O
</s>
<s>
Also	O
known	O
as	O
the	O
MOS	B-Architecture
transistor	I-Architecture
,	O
the	O
MOSFET	B-Architecture
is	O
the	O
most	O
widely	O
manufactured	O
device	O
in	O
the	O
world	O
.	O
</s>
<s>
The	O
concept	O
of	O
a	O
thin-film	O
transistor	O
(	O
TFT	O
)	O
was	O
first	O
proposed	O
by	O
John	O
Wallmark	O
who	O
in	O
1957	O
filed	O
a	O
patent	O
for	O
a	O
thin	O
film	O
MOSFET	B-Architecture
in	O
which	O
germanium	O
monoxide	O
was	O
used	O
as	O
a	O
gate	O
dielectric	O
.	O
</s>
<s>
The	O
TFT	O
is	O
a	O
special	O
type	O
of	O
MOSFET	B-Architecture
.	O
</s>
<s>
In	O
1986	O
,	O
Mitsubishi	O
Electric	O
researchers	O
H	O
.	O
Koezuka	O
,	O
A	O
.	O
Tsumura	O
and	O
Tsuneya	O
Ando	O
reported	O
the	O
first	O
organic	B-Algorithm
field-effect	I-Algorithm
transistor	I-Algorithm
,	O
based	O
on	O
a	O
polymer	B-Language
of	O
thiophene	O
molecules	O
.	O
</s>
<s>
The	O
thiophene	O
polymer	B-Language
is	O
a	O
type	O
of	O
conjugated	O
polymer	B-Language
that	O
is	O
able	O
to	O
conduct	O
charge	O
,	O
eliminating	O
the	O
need	O
to	O
use	O
expensive	O
metal	B-Architecture
oxide	I-Architecture
semiconductors	I-Architecture
.	O
</s>
<s>
Additionally	O
,	O
other	O
conjugated	O
polymers	B-Language
have	O
been	O
shown	O
to	O
have	O
semiconducting	O
properties	O
.	O
</s>
<s>
OFET	B-Algorithm
design	O
has	O
also	O
improved	O
in	O
the	O
past	O
few	O
decades	O
.	O
</s>
<s>
Many	O
OFETs	B-Algorithm
are	O
now	O
designed	O
based	O
on	O
the	O
thin-film	O
transistor	O
(	O
TFT	O
)	O
model	O
,	O
which	O
allows	O
the	O
devices	O
to	O
use	O
less	O
conductive	O
materials	O
in	O
their	O
design	O
.	O
</s>
<s>
One	O
common	O
feature	O
of	O
OFET	B-Algorithm
materials	O
is	O
the	O
inclusion	O
of	O
an	O
aromatic	O
or	O
otherwise	O
conjugated	O
π-electron	O
system	O
,	O
facilitating	O
the	O
delocalization	O
of	O
orbital	O
wavefunctions	O
.	O
</s>
<s>
OFETs	B-Algorithm
employing	O
many	O
aromatic	O
and	O
conjugated	O
materials	O
as	O
the	O
active	O
semiconducting	O
layer	O
have	O
been	O
reported	O
,	O
including	O
small	O
molecules	O
such	O
as	O
rubrene	O
,	O
tetracene	O
,	O
pentacene	O
,	O
diindenoperylene	B-Algorithm
,	O
perylenediimides	O
,	O
tetracyanoquinodimethane	O
(	O
TCNQ	O
)	O
,	O
and	O
polymers	B-Language
such	O
as	O
polythiophenes	B-Algorithm
(	O
especially	O
poly(3-hexylthiophene )	O
(	O
P3HT	B-Algorithm
)	O
)	O
,	O
polyfluorene	O
,	O
polydiacetylene	O
,	O
poly(2,5-thienylene vinylene )	O
,	O
poly(p-phenylene vinylene )	O
(	O
PPV	O
)	O
.	O
</s>
<s>
Rubrene-based	O
OFETs	B-Algorithm
show	O
the	O
highest	O
carrier	O
mobility	O
20	O
–	O
40cm2/	O
( V·s	O
)	O
.	O
</s>
<s>
Another	O
popular	O
OFET	B-Algorithm
material	O
is	O
pentacene	O
,	O
which	O
has	O
been	O
used	O
since	O
the	O
1980s	O
,	O
but	O
with	O
mobilities	O
10	O
to	O
100	O
times	O
lower	O
(	O
depending	O
on	O
the	O
substrate	O
)	O
than	O
rubrene	O
.	O
</s>
<s>
N-type	O
OFETs	B-Algorithm
are	O
yet	O
poorly	O
developed	O
.	O
</s>
<s>
They	O
are	O
MOSFET	B-Architecture
(	O
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
semiconductor	I-Architecture
field-effect	I-Architecture
transistor	I-Architecture
)	O
,	O
MESFET	O
(	O
metal	O
–	O
semiconductor	O
field-effect	O
transistor	O
)	O
and	O
TFT	O
(	O
thin-film	O
transistor	O
)	O
.	O
</s>
<s>
The	O
most	O
prominent	O
and	O
widely	O
used	O
FET	O
in	O
modern	O
microelectronics	O
is	O
the	O
MOSFET	B-Architecture
(	O
metal	B-Architecture
–	I-Architecture
oxide	I-Architecture
–	I-Architecture
semiconductor	I-Architecture
FET	O
)	O
.	O
</s>
<s>
There	O
are	O
different	O
kinds	O
in	O
this	O
category	O
,	O
such	O
as	O
MISFET	B-Architecture
(	O
metal	O
–	O
insulator	O
–	O
semiconductor	O
field-effect	O
transistor	O
)	O
,	O
and	O
IGFET	B-Architecture
(	O
insulated-gate	O
FET	O
)	O
.	O
</s>
<s>
A	O
schematic	O
of	O
a	O
MISFET	B-Architecture
is	O
shown	O
in	O
Figure	O
1a	O
.	O
</s>
<s>
The	O
only	O
difference	O
of	O
this	O
one	O
from	O
the	O
MISFET	B-Architecture
is	O
that	O
the	O
n-type	O
source	O
and	O
drain	O
are	O
connected	O
by	O
an	O
n-type	O
region	O
.	O
</s>
<s>
In	O
this	O
case	O
,	O
the	O
depletion	O
region	O
extends	O
all	O
over	O
the	O
n-type	O
channel	O
at	O
zero	O
gate	O
voltage	O
in	O
a	O
normally	O
“	O
off	O
”	O
device	O
(	O
it	O
is	O
similar	O
to	O
the	O
larger	O
positive	O
bias	O
in	O
MISFET	B-Architecture
case	O
)	O
.	O
</s>
<s>
OFETs	B-Algorithm
adopt	O
the	O
architecture	O
of	O
TFT	O
.	O
</s>
<s>
With	O
the	O
development	O
of	O
the	O
conducting	O
polymer	B-Language
,	O
the	O
semiconducting	O
properties	O
of	O
small	O
conjugated	O
molecules	O
have	O
been	O
recognized	O
.	O
</s>
<s>
The	O
interest	O
in	O
OFETs	B-Algorithm
has	O
grown	O
enormously	O
in	O
the	O
past	O
ten	O
years	O
.	O
</s>
<s>
The	O
performance	O
of	O
OFETs	B-Algorithm
,	O
which	O
can	O
compete	O
with	O
that	O
of	O
amorphous	O
silicon	O
(	O
a-Si	O
)	O
TFTs	O
with	O
field-effect	O
mobilities	O
of	O
0.5	O
–	O
1cm2	O
V−1	O
s−1	O
and	O
ON/OFF	O
current	O
ratios	O
(	O
which	O
indicate	O
the	O
ability	O
of	O
the	O
device	O
to	O
shut	O
down	O
)	O
of	O
106	O
–	O
108	O
,	O
has	O
improved	O
significantly	O
.	O
</s>
<s>
and	O
0.6cm2	O
V−1	O
s−1	O
for	O
solution-processed	O
polymers	B-Language
have	O
been	O
reported	O
.	O
</s>
<s>
As	O
a	O
result	O
,	O
there	O
is	O
now	O
a	O
greater	O
industrial	O
interest	O
in	O
using	O
OFETs	B-Algorithm
for	O
applications	O
that	O
are	O
currently	O
incompatible	O
with	O
the	O
use	O
of	O
a-Si	O
or	O
other	O
inorganic	O
transistor	O
technologies	O
.	O
</s>
<s>
One	O
of	O
their	O
main	O
technological	O
attractions	O
is	O
that	O
all	O
the	O
layers	O
of	O
an	O
OFET	B-Algorithm
can	O
be	O
deposited	O
and	O
patterned	O
at	O
room	O
temperature	O
by	O
a	O
combination	O
of	O
low-cost	O
solution-processing	O
and	O
direct-write	O
printing	O
,	O
which	O
makes	O
them	O
ideally	O
suited	O
for	O
realization	O
of	O
low-cost	O
,	O
large-area	O
electronic	O
functions	O
on	O
flexible	O
substrates	O
.	O
</s>
<s>
Thermally	O
oxidized	O
silicon	O
is	O
a	O
traditional	O
substrate	O
for	O
OFETs	B-Algorithm
where	O
the	O
silicon	O
dioxide	O
serves	O
as	O
the	O
gate	O
insulator	O
.	O
</s>
<s>
The	O
carrier	O
transport	O
in	O
OFET	B-Algorithm
is	O
specific	O
for	O
two-dimensional	O
(	O
2D	O
)	O
carrier	O
propagation	O
through	O
the	O
device	O
.	O
</s>
<s>
Whereas	O
carriers	O
propagate	O
through	O
polycrystalline	O
OFETs	B-Algorithm
in	O
a	O
diffusion-like	O
(	O
trap-limited	O
)	O
manner	O
,	O
they	O
move	O
through	O
the	O
conduction	O
band	O
in	O
the	O
best	O
single-crystalline	O
OFETs	B-Algorithm
.	O
</s>
<s>
The	O
most	O
important	O
parameter	O
of	O
OFET	B-Algorithm
carrier	O
transport	O
is	O
carrier	O
mobility	O
.	O
</s>
<s>
Its	O
evolution	O
over	O
the	O
years	O
of	O
OFET	B-Algorithm
research	O
is	O
shown	O
in	O
the	O
graph	O
for	O
polycrystalline	O
and	O
single	O
crystalline	O
OFETs	B-Algorithm
.	O
</s>
<s>
The	O
horizontal	O
lines	O
indicate	O
the	O
comparison	O
guides	O
to	O
the	O
main	O
OFET	B-Algorithm
competitors	O
–	O
amorphous	O
(	O
a-Si	O
)	O
and	O
polycrystalline	O
silicon	O
.	O
</s>
<s>
The	O
graph	O
reveals	O
that	O
the	O
mobility	O
in	O
polycrystalline	O
OFETs	B-Algorithm
is	O
comparable	O
to	O
that	O
of	O
a-Si	O
whereas	O
mobility	O
in	O
rubrene-based	O
OFETs	B-Algorithm
(	O
20	O
–	O
40cm2/	O
( V·s	O
)	O
)	O
approaches	O
that	O
of	O
best	O
poly-silicon	O
devices	O
.	O
</s>
<s>
Development	O
of	O
accurate	O
models	O
of	O
charge	O
carrier	O
mobility	O
in	O
OFETs	B-Algorithm
is	O
an	O
active	O
field	O
of	O
research	O
.	O
</s>
<s>
have	O
developed	O
an	O
analytical	O
model	O
of	O
carrier	O
mobility	O
in	O
OFETs	B-Algorithm
that	O
accounts	O
for	O
carrier	O
density	O
and	O
the	O
polaron	O
effect	O
.	O
</s>
<s>
While	O
average	O
carrier	O
density	O
is	O
typically	O
calculated	O
as	O
function	O
of	O
gate	O
voltage	O
when	O
used	O
as	O
an	O
input	O
for	O
carrier	O
mobility	O
models	O
,	O
modulated	O
amplitude	O
reflectance	O
spectroscopy	O
(	O
MARS	O
)	O
has	O
been	O
shown	O
to	O
provide	O
a	O
spatial	O
map	O
of	O
carrier	O
density	O
across	O
an	O
OFET	B-Algorithm
channel	O
.	O
</s>
